The present specification relates to a semiconductor device and a method of making a semiconductor device.
TrenchMOS semiconductor devices are commonly used for power applications. A TrenchMOS device typically includes a semiconductor substrate having a layer of epitaxially grown, doped silicon located thereon, in which is formed a trench containing a gate electrode and gate dielectric. A source region of the device is located adjacent an upper part of the trench. The device also includes a drain region, which is separated from the source region by a body region, through which the trench extends.
Manufacture of TrenchMOS devices generally includes processing the substrate by etching the trench into the layer of epitaxial silicon and by implanting ions to form the source and body regions.
The doping concentration of the layer of epitaxial silicon in which the device is formed is determined during the epitaxial growth process. Conventionally the epitaxial layer has a uniform doping concentration, although it is also known to use epitaxial silicon having a graded doping concentration to reduce the electric fields within the device to reduce the risk of device breakdown and improve long-term reliability. This graded doping concentration is achieved by varying the amount of, e.g. phosphorous per μm as the layer is grown.